High step coverage tungsten deposition

ABSTRACT

Methods of depositing a tungsten nucleation layers that achieve very good step coverage are provided. The methods involve a sequence of alternating pulses of a tungsten-containing precursor and a boron-containing reducing agent, while co-flowing hydrogen (H2) with the boron-containing reducing agent. The H2 flow is stopped prior to the tungsten-containing precursor flow. By co-flowing H2 with the boron-containing reducing agent but not with the tungsten-containing precursor flow, a parasitic CVD component is reduced, resulting in a more self-limiting process. This in turn improves step coverage and conformality of the nucleation layer. Related apparatuses are also provided.

INCORPORATION BY REFERENCE

A PCT Request Form is filed concurrently with this specification as partof the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed PCT Request Form is incorporated by reference hereinin its entirety and for all purposes.

BACKGROUND

Tungsten (W) film deposition using chemical vapor deposition (CVD)techniques is an integral part of semiconductor fabrication processes.For example, tungsten films may be used as low resistivity electricalconnections in the form of horizontal interconnects, vias betweenadjacent metal layers, and contacts between a first metal layer and thedevices on a silicon substrate. Tungsten films may also be used invarious memory applications, including in formation of buried wordline(bWL) architectures for dynamic random access memory (DRAM), word linesfor 3D NAND, and logic applications. However, the continued decrease infeature size and film thickness brings various challenges includingdeposition of films having good step coverage.

The background description provided herein is for the purposes ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

SUMMARY

One aspect of the disclosure relates to a method including providing asubstrate including a feature having an opening in a top surface, asidewall and a bottom in a chamber; and depositing a tungsten nucleationlayer in the feature by performing multiple cycles of: flowing aboron-containing reducing agent pulse in the chamber, wherein theboron-containing reducing agent is adsorbed to the feature sidewall andfeature bottom, purging the chamber, flowing a tungsten-containingprecursor pulse in the chamber to react with the adsorbedboron-containing reducing agent, and purging the chamber, whereinhydrogen (H₂) is flowed during the boron-containing reducing agent pulseand no H₂ is flowed during the tungsten-containing precursor pulse andwherein H₂ suppresses thermal decomposition of the boron-containingreducing agent.

In some embodiments, the tungsten nucleation layer is at least 10Angstroms thick and step coverage throughout the feature is at least90%, step coverage being the ratio of the thickness of the tungstennucleation layer at any point in the feature to the thickness of thetungsten nucleation layer at the top surface.

In some embodiments, depositing the nucleation layer further includes atleast one cycle of flowing a silane pulse in the chamber; purging thechamber; flowing a tungsten-containing precursor pulse in the chamber;and purging the chamber, wherein no hydrogen is flowed during thetungsten-containing precursor pulse.

In some embodiments, no hydrogen is flowed during the silane pulse. Insome embodiments, hydrogen is flowed during the silane pulse. In someembodiments, the tungsten nucleation layer is between 10 Angstroms and50 Angstroms thick. In some embodiments. the substrate temperature isbelow 350° C. In some embodiments, the substrate temperature is betweenabout 250° C. and 300° C. In some embodiments, hydrogen reacts withdecomposition byproducts of the boron-containing reducing agent.

In some embodiments, the boron-containing reducing agent pulse in thechamber is flowed into the chamber with an inert carrier gas.

In some embodiments, wherein the volumetric flow ratio of the H₂ to theboron-containing reducing agent is between 20:1 and 400:1. In someembodiments, the boron-containing reducing agent is diborane.

Another aspect of the disclosure relates to a method including providinga substrate including a feature having an opening in a top surface, asidewall and a bottom in a chamber; depositing a tungsten nucleationlayer in the feature by performing multiple cycles of: flowing aboron-containing reducing agent pulse in the chamber; purging thechamber; flowing a tungsten-containing precursor pulse in the chamber;and purging the chamber, wherein hydrogen is flowed during theboron-containing reducing agent pulse and no hydrogen is flowed duringthe tungsten-containing precursor pulse.

In some embodiments, the tungsten nucleation layer is at least 10Angstroms thick and step coverage throughout the feature is at least90%, step coverage being the ratio of the thickness of the tungstennucleation layer at any point in the feature to the thickness of thetungsten nucleation layer at the top surface.

In some embodiments, depositing the nucleation layer further includes atleast one cycle of flowing a silane pulse in the chamber; purging thechamber; flowing a tungsten-containing precursor pulse in the chamber;and purging the chamber, wherein no hydrogen is flowed during thetungsten-containing precursor pulse.

In some embodiments, no hydrogen is flowed during the silane pulse. Insome embodiments, hydrogen is flowed during the silane pulse. In someembodiments, the tungsten nucleation layer is between 10 Angstroms and50 Angstroms thick. In some embodiments. the substrate temperature isbelow 350° C. In some embodiments, the substrate temperature is betweenabout 250° C. and 300° C. In some embodiments, hydrogen reacts withdecomposition byproducts of the boron-containing reducing agent.

In some embodiments, the boron-containing reducing agent pulse in thechamber is flowed into the chamber with an inert carrier gas.

In some embodiments, the volumetric flow ratio of the H2 to theboron-containing reducing agent is between 20:1 and 400:1. In someembodiments, the boron-containing reducing agent is diborane.

Another aspect of the disclosure relates to an apparatus including: (a)a process chamber including at least one station having a pedestalconfigured to hold a substrate; (b) at least one outlet for coupling toa vacuum; (c) one or more process gas inlets coupled to one or moreprocess gas sources; and (d) a controller for controlling operations inthe apparatus, including machine-readable instructions for: flowing aboron-containing reducing agent pulse in the chamber, purging thechamber, flowing a tungsten-containing precursor pulse in the chamber,and purging the chamber, wherein hydrogen is flowed during theboron-containing reducing agent pulse and no hydrogen is flowed duringthe tungsten-containing precursor pulse.

In some embodiments, the controller includes instructions formaintaining a pedestal temperature less than 350° C. In someembodiments, the controller includes instructions for maintaining apedestal temperature between 175° C. to 300° C. In some embodiments, thecontroller includes instructions for flowing a silane pulse in thechamber; purging the chamber; flowing a tungsten-containing precursorpulse in the chamber; and purging the chamber, wherein no hydrogen isflowed during the tungsten-containing precursor pulse.

These and other aspects are described below with reference to thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1H show examples of a features that may be filled with tungstenin accordance with embodiments disclosed herein.

FIG. 2 shows a timing sequence diagram showing example cycles of amethod for depositing a tungsten nucleation layer using diborane.

FIG. 3 illustrates a schematic representation of an example of a featureprovided in a partially manufactured semiconductor substrate with atungsten nucleation layer formed with the feature.

FIG. 4 is a schematic of an example of a process system suitable forconducting deposition processes in accordance with embodiments.

FIG. 5 is a schematic of an example of a deposition station depictedsuitable for conducting deposition processes in accordance withembodiments.

FIG. 6 is a schematic of an example of a manifold system that may beused in accordance with various embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Thepresent invention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail to not unnecessarily obscure the present invention.While the invention will be described in conjunction with the specificembodiments, it will be understood that it is not intended to limit theinvention to the embodiments.

Described herein are methods of filling features with tungsten andrelated systems and apparatus. Examples of application include logic andmemory contact fill, DRAM buried wordline fill, vertically integratedmemory gate/wordline fill, and 3-D integration with through-silicon vias(TSVs). The methods described herein can be used to fill verticalfeatures, such as in tungsten vias, and horizontal features, such asvertical NAND (VNAND) wordlines, and The methods may be used forconformal and bottom-up or inside-out fill.

According to various embodiments, the features can be characterized byone or more of narrow and/or re-entrant openings, constrictions withinthe feature, and high aspect ratios. Examples of features that can befilled are depicted in FIGS. 1A-1C. FIG. 1A shows an example of across-sectional depiction of a vertical feature 101 to be filled withtungsten. The feature can include a feature hole 105 in a substrate 103.The substrate may be a silicon wafer, e.g., 200-mm wafer, 300-mm wafer,450-mm wafer, including wafers having one or more layers of materialsuch as dielectric, conducting, or semi-conducting material depositedthereon. In some embodiments, the feature hole 105 may have an aspectratio of at least about 2:1, at least about 4:1, at least about 6:1 orhigher. The feature hole 105 may also have a dimension near the opening,e.g., an opening diameter or line width, of between about 10 nm to 500nm, for example between about 25 nm to 300 nm. The feature hole 105 canbe referred to as an unfilled feature or simply a feature. The feature,and any feature, may be characterized in part by an axis 118 thatextends through the length of the feature, with vertically-orientedfeatures having vertical axes and horizontally-oriented features havinghorizontal axes.

FIG. 1B shows an example of a feature 101 that has a re-entrant profile.A re-entrant profile is a profile that narrows from a bottom, closedend, or interior of the feature to the feature opening. According tovarious embodiments, the profile may narrow gradually and/or include anoverhang at the feature opening. FIG. 1B shows an example of the latter,with an under-layer 113 lining the sidewall or interior surfaces of thefeature hole 105. The under-layer 113 can be for example, a diffusionbarrier layer, an adhesion layer, a nucleation layer, a combination ofthereof, or any other applicable material. The under-layer 113 forms anoverhang 115 such that the under-layer 113 is thicker near the openingof the feature 101 than inside the feature 101.

In some embodiments, features having one or more constrictions withinthe feature may be filled. FIG. 1C shows examples of views of variousfilled features having constrictions. Each of the examples (a), (b) and(c) in FIG. 1C includes a constriction 109 at a midpoint within thefeature. The constriction 109 can be, for example, between about 15nm-20 nm wide. Constrictions can cause pinch off during deposition oftungsten in the feature using conventional techniques, with depositedtungsten blocking further deposition past the constriction before thatportion of the feature is filled, resulting in voids in the feature.Example (b) further includes a liner/barrier overhang 115 at the featureopening. Such an overhang could also be a potential pinch-off point.Example (c) includes a constriction 112 further away from the fieldregion than the overhang 115 in example (b). As described further below,methods described herein allow void-free fill as depicted in FIG. 1C.

Horizontal features, such as in 3-D memory structures, can also befilled. FIG. 1D shows an example of a word line 150 in a VNAND structure148 that includes a constriction 151. In some embodiments, theconstrictions can be due to the presence of pillars in a VNAND or otherstructure. FIG. 1E, for example, shows a plan view of pillars 125 in aVNAND structure, with FIG. 1F showing a simplified schematic of across-sectional depiction of the pillars 125. Arrows in FIG. 1Erepresent deposition material; as pillars 125 are disposed between anarea 127 and a gas inlet or other deposition source, adjacent pillarscan result in constrictions that present challenges in void free fill ofan area 127.

FIG. 1G provides another example of a view horizontal feature, forexample, of a VNAND or other structure including pillar constrictions151. The example in FIG. 1G is open-ended, with material to be depositedable to enter laterally from two sides as indicated by the arrows. (Itshould be noted that example in FIG. 1G can be seen as a 2-D rendering3-D features of the structure, with the FIG. 1G being a cross-sectionaldepiction of an area to be filled and pillar constrictions shown in thefigure representing constrictions that would be seen in a plan ratherthan cross-sectional view.) In some embodiments, 3-D structures can becharacterized with the area to be filled extending along threedimensions (e.g., in the X, Y and Z-directions in the example of FIG.1F), and can present more challenges for fill than filling holes ortrenches that extend along one or two dimensions. For example,controlling fill of a 3-D structure can be challenging as depositiongasses may enter a feature from multiple dimensions. The methods mayalso be used to fill interconnects to tungsten wordlines as shown inFIG. 1H, where interconnect features 170 may be filled with tungsten toconnect to the tungsten wordlines 172. Examples of feature fill forhorizontally-oriented and vertically-oriented features are describedbelow. It should be noted that in most cases, the examples applicable toboth horizontally-oriented or vertically-oriented features.

Distribution of a material within a feature may be characterized by itsstep coverage. For the purposes of this description, “step coverage” isdefined as a ratio of two thicknesses, e.g., the thickness of thematerial inside the feature divided by the thickness of the materialnear the opening. For purposes of this description, the term “inside thefeature” represents a middle portion of the feature located about themiddle point of the feature along the feature's axis, e.g., an areabetween about 25% and 75% of the distance or, in certain embodiments,between about 40% and 60% of the distance along the feature's depthmeasured from the feature's opening, or an end portion of the featurelocated between about 75% and 95% of the distance along the feature'saxis as measured from the opening. The term “near the opening of thefeature” or “near the feature's opening” represents a top portion of thefeature located within 25% or, more specifically, within 10% of theopening's edge or other element representative of the opening's edge.Step coverage of over 100% can be achieved, for example, by filling afeature wider in the middle or near the bottom of the feature than atthe feature opening or where a thicker film is deposited within thefeature than on or near the opening.

The methods described herein involve deposition of a tungsten nucleationlayer prior to deposition of a bulk layer. A nucleation layer istypically a thin conformal layer that facilitates subsequent depositionof bulk tungsten-containing material thereon. According to variousembodiments, a nucleation layer may be deposited prior to any fill ofthe feature and/or at subsequent points during fill of the feature withtungsten or a tungsten-containing material.

In certain implementations, the nucleation layer is depositedsequentially injecting pulses of a reducing agent, optional purge gases,and tungsten-containing precursor from the reaction chamber. The processis repeated in a cyclical fashion until the desired thickness isachieved. Nucleation layer thickness can depend on the nucleation layerdeposition method as well as the desired quality of bulk deposition. Ingeneral, nucleation layer thickness is sufficient to support highquality, uniform bulk deposition. Examples may range from 5Å-100Å, or12Å-50Å.

ALD techniques differ from chemical vapor deposition (CVD) techniques inwhich reactants are introduced together. In certain embodiments, thenucleation layer is deposited using a pulsed nucleation layer (PNL)technique. In a PNL technique, pulses of a reducing agent, optionalpurge gases, and tungsten-containing precursor are sequentially injectedinto and purged from the reaction chamber. The process is repeated in acyclical fashion until the desired thickness is achieved. PNL broadlyembodies any cyclical process of sequentially adding reactants forreaction on a semiconductor substrate, including ALD techniques.

Described herein are methods of depositing a tungsten nucleation layerthat achieve very good step coverage. The methods involve a sequence ofalternating pulses of a tungsten-containing precursor and aboron-containing reducing agent, while co-flowing hydrogen (H₂) with theboron-containing reducing agent. The H₂ flow is stopped prior to thetungsten-containing precursor flow. By co-flowing H₂ with theboron-containing reducing agent but not with the tungsten-containingprecursor flow, a parasitic CVD component is reduced, resulting in amore self-limiting process. This in turn improves step coverage andconformality of the nucleation layer.

ALD tungsten processes may use two half-reactions enabled by thesequential delivery of two or more co-reactants. One co-reactant acts tofunctionalize the surface and permit the adsorption oftungsten-containing species to the substrate. Subsequent cycles resultin the deposition of a conformal thin film. Flowing hydrogen in thebackground or as a carrier gas during the tungsten-containing precursordose results in a higher deposition rate, thicker nucleation layer, andreduced conformality. This is due to part of the tungsten-containingprecursor being consumed by a parasitic CVD reaction with the hydrogen.However, it has been found that co-flowing H₂ with B₂H₆ improvesconformality. This is because B₂H₆ can decompose during the ALD cycle(e.g., B₂H₆→⅔B₃+3H₂) which in turn results in parasitic reactions thatcontribute to the CVD reaction. The parasitic CVD contribution degradesthe step coverage of the process. By co-flowing B₂H₆ and H₂, thedecomposition of B₂H₆ is suppressed. While some B₂H₆ may decompose, thepresence of H₂ can significantly reduce the amount. Further, the H₂ mayreact with B₂H₆ decomposition products or other reaction byproducts toform diborane (e.g., 2B₃+9H₂→3B₂H₆). The parasitic CVD contribution tothe deposition is thus reduced or minimized. This shifts the thin filmdeposition process closer to a pure ALD process and improves the stepcoverage and conformality.

By flowing hydrogen with the diborane, chemisorption and physisorptionof the diborane, rather than decomposition of diborane to boron, ispromoted. This is distinct from other deposition processes that use aboron sacrificial layer.

Substrate temperatures may be below about 350° C., for example betweenabout 175° C. and 300° C., or between about 250° C. and 300° C. Lowertemperatures result in less decomposition and more control over thedeposition. Even at these relatively low temperatures, diborane issusceptible to decomposition. Examples of chamber pressure are between10 torr and 60 torr, or 10 torr and 40 torr. In some embodiments, it isabove 10 torr. It may also be below 10 torr to reduce fluorineincorporation, for example.

Example growth rates may be 2 Å-20 Å per cycle, or 4 Å-12 Å per cycle,with the growth rates lower as more hydrogen is used to suppress theparasitic CVD reaction and increase step coverage.

The hydrogen:diborane volumetric flow ratio may be tuned to provide thedesired effect for a particular structure. Too high, and thephysisorption or chemisorption of the diborane may be unnecessarilyslow. Too low, and the diborane may decompose, causing the parasitic CVDeffect described above. Examples of ranges of H₂:B₂H₆ are 20:1-400:1.

In some embodiments, the diborane (or other reducing agent) is deliveredwith an inert gas. For example, B₂H₆ may be mixed with nitrogen (N₂) ina 20:1 N₂:B₂H₆ ratio. The H₂ to diborane/inert gas mixture may be1:1-20:1 to obtain 20:1-400:1 H₂:B₂H₆ in that example. Nitrogen is anexample of gas that may be mixed with diborane or other reducing agent;any inert gas that is chemically compatible with the reducing agent anddoes not react with it may be used, with helium (He) another example.

FIG. 2 shows an example of a timing sequence diagram showing examplecycles of a method for depositing a tungsten nucleation layer usingdiborane. As shown in FIG. 2, hydrogen is flowed only during thediborane pulse.

The tungsten nucleation layers may be deposited using a silicon-basedprecursor (e.g., silane, SiH4) in addition to diborane. In someembodiments, silane pulses are added as part of the sequence: e.g.,B/W/B/W/S/W, where B represents a diborane pulse, W atungsten-containing precursor pulses, and S a silicon-containingprecursors pulse; intervening purges are not explicitly shown. In suchembodiments, silane or other silicon-containing precursor may be pulsedwithout hydrogen.

The tungsten-containing precursor may be a tungsten halide that can bereduced by a boron-containing reducing agent including tungstenfluorides (e.g., WF6) and tungsten chlorides (e.g., WCl5 and WCl6).While the diborane is described above, the method may be implementedwith any reducing agent that is susceptible to decomposition at ALDprocessing temperatures. Examples include hexaborane and triborane.

In some embodiments, methods result in step coverages of at least 90%.FIG. 3 illustrates a schematic representation of a feature 301 providedin a partially manufactured semiconductor substrate 303 with a tungstennucleation layer 305 formed with the feature 301. The figure alsospecifies different points of measurements of the layer thickness,including at the top of the feature, the bottom of the feature, and atvarious sidewall depths, as measured as % of feature depth. Stepcoverage is measured as the ratio of the thickness at a bottom orsidewall position to the top position, unless otherwise indicated.

Although the description herein refers to tungsten nucleation layerdeposition using diborane, pulsing hydrogen with a co-reactant may beperformed to improve conformality during ALD deposition of othermaterials and other co-reactants, when the co-reactants are susceptibleto decomposition and are hydrides. Examples of other metals that may bedeposited include molybdenum (Mo) and ruthenium (Ru).

Experimental

ALD of tungsten nucleation layers was performed in features usingProcesses A and B on structures of the same dimensions:

Process A: multiple cycles of (B₂H₆-Ar purge-WF₆-Ar purge) with H2 flowconstant

Process B: multiple cycles of (B₂H₆-Ar purge-WF₆-Ar purge) with H2 flowconstant only during B₂H₆ pulses.

Step coverage was measured at the top sidewall, middle sidewall andbottom sidewall with respect to the film deposited on the top horizontalsurface. The top sidewall refers to a point about 5% of feature depth,middle about 50%, and bottom about 95% of feature depth.

Process A Process B Top sidewall 91.7% 98.8% Middle sidewall 70.8%  100%Bottom sidewall 58.3% 91.8%

As can be seen from the above table, co-flowing H2 only during the B2H6pulses results in significantly improved step coverage. A third processwas used on a different structure: Process C: multiple cycles of(B₂H₆-Ar purge-WF₆-Ar purge) with no H₂ at all:

Process C Top sidewall 83% Middle sidewall 74% Bottom sidewall 66%

After nucleation layer deposition, the feature may be filled with a bulktungsten layer. In some implementations, tungsten bulk deposition canoccur by a CVD process in which a reducing agent and atungsten-containing precursor are flowed into a deposition chamber todeposit a bulk fill layer in the feature. In some implementations,tungsten bulk deposition can occur by an ALD process in which a reducingagent and a tungsten-containing precursor are sequentially introducedinto a deposition chamber to deposit a bulk fill layer in the feature.If CVD is used, this operation can involve flowing the reactantscontinuously until the desired amount is deposited. In certainimplementations, the CVD operation may take place in multiple stages,with multiple periods of continuous and simultaneous flow of reactantsseparated by periods of one or more reactant flows diverted. Stillfurther, inhibition of tungsten growth and/or etching may be performedduring feature fill.

Various tungsten containing gases including, but not limited to, WF6,WCl6, and W(CO)6 can be used as the tungsten-containing precursor. Incertain implementations, the tungsten-containing precursor is ahalogen-containing compound, such as WF6. In certain implementations,the reducing agent is hydrogen gas, though other reducing agents may beused including silane (SiH₄), disilane (Si₂H₆) hydrazine (N₂H₄),diborane (B₂H₆) and germane (GeH₄). In many implementations, hydrogengas is used as the reducing agent in the CVD process. In some otherimplementations, a tungsten precursor that can decompose to form a bulktungsten layer can be used. Bulk deposition may also occur using othertypes of processes including ALD processes.

Deposition may proceed according to various implementations until acertain feature profile is achieved and/or a certain amount of tungstenis deposited. In some implementations, the deposition time and otherrelevant parameters may be determined by modeling and/or trial anderror. For example, for an initial deposition for an inside out fillprocess in which tungsten can be conformally deposited in a featureuntil pinch-off, it may be straightforward to determine based on thefeature dimensions the tungsten thickness and corresponding depositiontime that will achieve pinch-off. In some implementations, a processchamber may be equipped with various sensors to perform in-situmetrology measurements for end-point detection of a depositionoperation. Examples of in-situ metrology include optical microscopy andX-Ray Fluorescence (XRF) for determining thickness of deposited films.

It should be understood that the tungsten films described herein mayinclude some amount of other compounds, dopants and/or impurities suchas nitrogen, carbon, oxygen, boron, phosphorous, sulfur, silicon,germanium and the like, depending on the particular precursors andprocesses used. The tungsten content in the film may range from 20% to100% (atomic) tungsten. In many implementations, the films aretungsten-rich, having at least 50% (atomic) tungsten, or even at leastabout 60%, 75%, 90%, or 99% (atomic) tungsten. In some implementations,the films may be a mixture of metallic or elemental tungsten (W) andother tungsten-containing compounds such as tungsten carbide (WC),tungsten nitride (WN), etc.

CVD and ALD deposition of these materials can include using anyappropriate precursors. For example, CVD and ALD deposition of tungstennitride can include using halogen-containing and halogen-freetungsten-containing and nitrogen-containing compounds.

Apparatus

Any suitable chamber may be used to implement the disclosed embodiments.Example deposition apparatuses include various systems, e.g., ALTUS® andALTUS® Max, available from Lam Research Corp., of Fremont, Calif., orany of a variety of other commercially available processing systems. Insome embodiments, atomic layer deposition (ALD) may be performed at afirst station that is one of two, five, or even more deposition stationspositioned within a single deposition chamber. Thus, for example, adiborane (B₂H₆)/hydrogen (H2) co-flow and tungsten hexafluoride (WF6)may be introduced in alternating pulses to the surface of thesemiconductor substrate, at the first station, using an individual gassupply system that creates a localized atmosphere at the substratesurface. Another station may be used for tungsten bulk layer deposition.Two or more stations may be used to deposit tungsten in parallelprocessing. Alternatively a wafer may be indexed to have operationsperformed over two or more stations sequentially.

FIG. 4 is a schematic of a process system suitable for conductingdeposition processes in accordance with embodiments. The system 400includes a transfer module 403. The transfer module 403 provides aclean, pressurized environment to minimize risk of contamination ofsubstrates being processed as they are moved between various reactormodules. Mounted on the transfer module 403 is a multi-station reactor409 capable of performing ALD and CVD according to various embodiments.Multi-station reactor 409 may include multiple stations 411, 413, 415,and 417 that may sequentially perform operations in accordance withdisclosed embodiments. For example, multi-station reactor 409 may beconfigured such that station 411 performs a tungsten nucleation layerdeposition using a chlorine-containing tungsten precursor or afluorine-containing precursor, and station 413 performs an ALD tungstendeposition operation according to various embodiments. In someembodiments, station 415 may also form an ALD tungsten depositionoperation, and station 417 may perform a CVD operation.

Stations may include a heated pedestal or substrate support, one or moregas inlets or showerhead or dispersion plate. An example of a depositionstation 500 is depicted in FIG. 5, including substrate support 502 andshowerhead 503. A heater may be provided in pedestal portion 501.

Returning to FIG. 4, also mounted on the transfer module 403 may be oneor more single or multi-station modules 407 capable of performing plasmaor chemical (non-plasma) pre-cleans, other deposition operations, oretch operations. The module may also be used for various treatments to,for example, prepare a substrate for a deposition process. The system400 also includes one or more wafer source modules 401, where wafers arestored before and after processing. An atmospheric robot (not shown) inthe atmospheric transfer chamber 419 may first remove wafers from thesource modules 401 to loadlocks 421. A wafer transfer device (generallya robot arm unit) in the transfer module 403 moves the wafers fromloadlocks 421 to and among the modules mounted on the transfer module403.

In various embodiments, a system controller 429 is employed to controlprocess conditions during deposition. The controller 429 will typicallyinclude one or more memory devices and one or more processors. Aprocessor may include a CPU or computer, analog and/or digitalinput/output connections, stepper motor controller boards, etc.

The controller 429 may control all of the activities of the depositionapparatus. The system controller 429 executes system control software,including sets of instructions for controlling the timing, mixture ofgases, chamber pressure, chamber temperature, wafer temperature, radiofrequency (RF) power levels, wafer chuck or pedestal position, and otherparameters of a particular process. Other computer programs stored onmemory devices associated with the controller 429 may be employed insome embodiments.

Typically there will be a user interface associated with the controller429. The user interface may include a display screen, graphical softwaredisplays of the apparatus and/or process conditions, and user inputdevices such as pointing devices, keyboards, touch screens, microphones,etc.

System control logic may be configured in any suitable way. In general,the logic can be designed or configured in hardware and/or software. Theinstructions for controlling the drive circuitry may be hard coded orprovided as software. The instructions may be provided by “programming.”Such programming is understood to include logic of any form, includinghard coded logic in digital signal processors, application-specificintegrated circuits, and other devices which have specific algorithmsimplemented as hardware. Programming is also understood to includesoftware or firmware instructions that may be executed on a generalpurpose processor. System control software may be coded in any suitablecomputer readable programming language.

The computer program code for controlling the germanium-containingreducing agent pulses, hydrogen flow, and tungsten-containing precursorpulses, and other processes in a process sequence can be written in anyconventional computer readable programming language: for example,assembly language, C, C++, Pascal, Fortran, or others. Compiled objectcode or script is executed by the processor to perform the tasksidentified in the program. Also as indicated, the program code may behard coded.

The controller parameters relate to process conditions, such as, forexample, process gas composition and flow rates, temperature, pressure,cooling gas pressure, substrate temperature, and chamber walltemperature. These parameters are provided to the user in the form of arecipe, and may be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of the system controller 429. The signals forcontrolling the process are output on the analog and digital outputconnections of the deposition apparatus 400.

The system software may be designed or configured in many differentways. For example, various chamber component subroutines or controlobjects may be written to control operation of the chamber componentsnecessary to carry out the deposition processes in accordance with thedisclosed embodiments. Examples of programs or sections of programs forthis purpose include substrate positioning code, process gas controlcode, pressure control code, and heater control code.

In some implementations, a controller 429 is part of a system, which maybe part of the above-described examples. Such systems can includesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller 429, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings in some systems, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller 429, in some implementations, may be a part of or coupledto a computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller 429 may be in the “cloud” or all or a part of a fab hostcomputer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by including one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a CVD chamber or module, an ALD chamber or module, an atomiclayer etch (ALE) chamber or module, an ion implantation chamber ormodule, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The controller 429 may include various programs. A substrate positioningprogram may include program code for controlling chamber components thatare used to load the substrate onto a pedestal or chuck and to controlthe spacing between the substrate and other parts of the chamber such asa gas inlet and/or target. A process gas control program may includecode for controlling gas composition, flow rates, pulse times, andoptionally for flowing gas into the chamber prior to deposition in orderto stabilize the pressure in the chamber. A pressure control program mayinclude code for controlling the pressure in the chamber by regulating,e.g., a throttle valve in the exhaust system of the chamber. A heatercontrol program may include code for controlling the current to aheating unit that is used to heat the substrate. Alternatively, theheater control program may control delivery of a heat transfer gas suchas helium to the wafer chuck.

Examples of chamber sensors that may be monitored during depositioninclude mass flow controllers, pressure sensors such as manometers, andthermocouples located in the pedestal or chuck. Appropriately programmedfeedback and control algorithms may be used with data from these sensorsto maintain desired process conditions.

The apparatus may include a gas manifold system, which provides linecharges to the various gas distribution lines as shown schematically inFIG. 6. Manifold 604 has inputs from a source 601 of atungsten-containing precursor gas, which may include an accumulator (notshown), which can also be referred to as a charge volume. Manifold 611has an input from a source 609 of hydrogen (H2) and a source 610 ofdiborane-containing mixture or other reducing gas (not shown). Both ofthese sources may include an accumulator (not shown). Manifold 621 hasan input from a source 619 of purge gas, which also may include anaccumulator. The manifolds 604, 611 and 6521 provide tungsten-containingprecursor gas, co-reactant gas, and purge gas to the deposition chamberthrough valved distribution lines, 605, 613 and 625 respectively. Thevarious valves may be opened or closed to provide a line charge, i.e.,to pressurize the distribution lines. For example, to pressurizedistribution line 605, valve 606 is closed to vacuum and valve 608 isclosed. After a suitable increment of time, valve 608 is opened and theco-flow gas is delivered to the chamber. After a suitable time fordelivery of the gas, valve 608 is closed. The chamber can then be purgedto a vacuum by opening of valve 606 to vacuum.

Similar processes can be used to deliver the reducing gas. To introducethe reducing gas, for example, distribution line 613 is charged byclosing valve 615 and closing valve 617 to vacuum. Opening of valve 615allows for delivery of the reducing gas to the chamber.

Similarly, to introduce the purge gas, distribution line 625 is chargedby closing valve 627 and closing valve 623 to vacuum. Opening of valve627 allows for delivery of the argon or other inert purge gas to thechamber.

The diborane or other reducing gas can be mixed with hydrogen at anypoint in the process and is not limited to the arrangement of FIG. 6.For example, a hydrogen/diborane mixture as stored may be used.Alternatively, it may be obtained from separate sources but mixed duringthe process at some point before delivery to the chamber or may bedelivered separately to the chamber with mixing occurring in thechamber.

FIG. 6 also shows vacuum pumps in which valves 606, 617 and 623,respectively, can be opened to purge the system. The supply of gasthrough the various distribution lines is controlled by a controller,such as a mass flow controller which is controlled by a microprocessor,a digital signal processor or the like, that is programmed with the flowrates, duration of the flow, and the sequencing of the processes.

Note that the processes described above may require precise timing ofvalves and mass flow controllers (MFCs) supplying pulses of reagent tothe semiconductor substrate during deposition. In one way to make thispossible, valve and MFC commands are delivered to embedded digitalinput-output controllers (IOC) in discrete packets of informationcontaining instructions for all time-critical commands for all or a partof a deposition sequence. The ALTUS systems of Lam Research provide atleast one IOC sequence. The IOCs can be physically located at variouspoints in the apparatus; e.g., within the process module or on astand-alone power rack standing some distance away from the processmodule. There may be multiple IOCs in each module (e.g., 3 per module).With respect to the actual instructions included in a sequence, allcommands for controlling valves and setting flow for MFCs (for allcarrier and reactant gases) may be included in a single IOC sequence.This assures that the timing of all the devices is tightly controlledfrom an absolute standpoint and also relative to each other. There aretypically multiple IOC sequences running at any given time. This allowsfor, say, ALD to run at station 1-2 with all timing controlled for allthe hardware components needed to deposit a ALD nucleation layer atthose stations. A second sequence might be running concurrently todeposit a bulk metal at other deposition stations in the same module.The relative timing of the devices controlling the delivery of reagentsto stations 3-4 is important within that group of devices, but therelative timing of the ALD process at stations 1-2 can be offset fromthe relative timing of stations 3-4. An IOC translates the informationin a packetized sequence and delivers digital or analog command signalsdirectly to MFC or pneumatic solenoid banks controlling the valves.

A pulse of tungsten-containing precursor gas may be generated asfollows. Initially, the system diverts WF6 to a vacuum pump for a periodof time while the MFC or other flow-controlling device stabilizes. Thismay be done for a period of between about 0.5 to 5 seconds in oneexample. Next, the system pressurizes the tungsten gas delivery manifoldby closing both the valve 606 to vacuum and the valve 608 to thedeposition chamber. This may be done for a period of between about 0.1and 5 seconds, for example, to create an initial burst of reagent whenthe valve to the deposition chamber is opened. This is accomplished byopening valve 508 for between about 0.1 and 10 seconds in one example.

Thereafter, the tungsten-containing gas is purged from the depositionchamber using a suitable purge gas. Similar to above, the system maypressurize the purge gas delivery manifold by closing valve 623 andvalve 627. Valves to an accumulator (not shown) are also closed topermit the accumulator to pressurize. This may be done for a period ofbetween about 0.1 and 5 seconds, for example, to rapidly flush reagentfrom the deposition chamber when the valve to the deposition chamber isopened. When valve 527 is opened to the deposition chamber, anaccumulator outlet valve is opened simultaneously or shortly thereafterto increase the mass flow of purge gas into the deposition chamber.Multiple accumulators may be used sequentially flow pressurized the samereactant or purge gas into the chamber during a single pulse operation.This can increases the overall mass flow rate.

The foregoing describes implementation of disclosed embodiments in asingle or multi-chamber semiconductor processing tool. The apparatus andprocess described herein may be used in conjunction with lithographicpatterning tools or processes, for example, for the fabrication ormanufacture of semiconductor devices, displays, LEDs, photovoltaicpanels, and the like. Typically, though not necessarily, suchtools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallyincludes some or all of the following steps, each step provided with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

1. A method comprising: providing a substrate including a feature havingan opening in a top surface, a sidewall and a bottom in a chamber; anddepositing a tungsten nucleation layer in the feature by performingmultiple cycles of: flowing a boron-containing reducing agent pulse inthe chamber, wherein the boron-containing reducing agent is adsorbed tothe feature sidewall and feature bottom, purging the chamber, flowing atungsten-containing precursor pulse in the chamber to react with theadsorbed boron-containing reducing agent, and purging the chamber,wherein hydrogen (H₂) is flowed during the boron-containing reducingagent pulse and no H₂ is flowed during the tungsten-containing precursorpulse, wherein H₂ suppresses thermal decomposition of theboron-containing reducing agent.
 2. The method of claim 1, wherein thetungsten nucleation layer is at least 10 Angstroms thick and stepcoverage throughout the feature is at least 90%, step coverage being theratio of the thickness of the tungsten nucleation layer at any point inthe feature to the thickness of the tungsten nucleation layer at the topsurface.
 3. The method of claim 1, wherein depositing the nucleationlayer further comprises at least one cycle of flowing a silane pulse inthe chamber; purging the chamber; flowing a tungsten-containingprecursor pulse in the chamber; and purging the chamber, wherein nohydrogen is flowed during the tungsten-containing precursor pulse. 4.The method of claim 3, wherein no hydrogen is flowed during the silanepulse.
 5. The method of claim 3, wherein hydrogen is flowed during thesilane pulse.
 6. The method of claim 1, wherein the tungsten nucleationlayer is between 10 Angstroms and 50 Angstroms thick.
 7. The method ofclaim 1, wherein the substrate temperature is below 350° C.
 8. Themethod of claim 1, wherein the substrate temperature is between about250° C. and 300° C.
 9. The method of claim 1, wherein hydrogen reactswith decomposition byproducts of the boron-containing reducing agent.10. The method of claim 1, wherein the boron-containing reducing agentpulse in the chamber is flowed into the chamber with an inert carriergas.
 11. The method of claim 1, wherein the volumetric flow ratio of theH₂ to the boron-containing reducing agent is between 20:1 and 400:1. 12.The method of claim 1, wherein the boron-containing reducing agent isdiborane.
 13. A method comprising: providing a substrate including afeature having an opening in a top surface, a sidewall and a bottom in achamber; depositing a tungsten nucleation layer in the feature byperforming multiple cycles of: flowing a boron-containing reducing agentpulse in the chamber; purging the chamber; flowing a tungsten-containingprecursor pulse in the chamber; and purging the chamber, whereinhydrogen is flowed during the boron-containing reducing agent pulse andno hydrogen is flowed during the tungsten-containing precursor pulse.14. An apparatus comprising: (a) a process chamber comprising at leastone station having a pedestal configured to hold a substrate; (b) atleast one outlet for coupling to a vacuum; (c) one or more process gasinlets coupled to one or more process gas sources; and (d) a controllerfor controlling operations in the apparatus, comprising machine-readableinstructions for: flowing a boron-containing reducing agent pulse in thechamber; purging the chamber; flowing a tungsten-containing precursorpulse in the chamber; and purging the chamber, wherein hydrogen isflowed during the boron-containing reducing agent pulse and no hydrogenis flowed during the tungsten-containing precursor pulse.
 15. Theapparatus of claim 14, wherein the controller comprises instructions formaintaining a pedestal temperature less than 350° C.
 16. The apparatusof claim 14, wherein the controller comprises instructions formaintaining a pedestal temperature between 175° C. to 300° C.
 17. Theapparatus of claim 14, wherein the controller comprises instructions forflowing a silane pulse in the chamber; purging the chamber; flowing atungsten-containing precursor pulse in the chamber; and purging thechamber, wherein no hydrogen is flowed during the tungsten-containingprecursor pulse.